Monthly Notices of the Royal Astronomical Society, Sep 27, 2019
The formation and evolution of local brightest cluster galaxies (BCGs) is investigated by determi... more The formation and evolution of local brightest cluster galaxies (BCGs) is investigated by determining the stellar populations and dynamics from the galaxy core, through the outskirts and into the intracluster light (ICL). Integral spectroscopy of 23 BCGs observed out to 4 r e is collected and high signal-to-noise regions are identified. Stellar population synthesis codes are used to determine the age, metallicity, velocity, and velocity dispersion of stars within each region. The ICL spectra are best modelled with populations that are younger and less metalrich than those of the BCG cores. The average BCG core age of the sample is 13.3 ± 2.8 Gyr and the average metallicity is [Fe/H] = 0.30 ± 0.09, whereas for the ICL the average age is 9.2 ± 3.5 Gyr and the average metallicity is [Fe/H] = 0.18 ± 0.16. The velocity dispersion profile is seen to be rising or flat in most of the sample (17/23), and those with rising values reach the value of the host cluster's velocity dispersion in several cases. The most extended BCGs are closest to the peak of the cluster's X-ray luminosity. The results are consistent with the idea that the BCG cores and inner regions formed quickly and long ago, with the outer regions and ICL forming more recently, and continuing to assemble through minor merging. Any recent star formation in the BCGs is a minor component, and is associated with the cluster cool core status.
A numerical study is presented of fragmentation in its simplest possible form: that of elongated,... more A numerical study is presented of fragmentation in its simplest possible form: that of elongated, isothermal, axially symmetric clouds. Results have been obtained for different ratios of length to diameter, L/D, and initial Jeans numbers, J0 (ratio of gravitational to thermal energies). Initial density perturbations are introduced on the axis of otherwise uniformly dense cylinders, and the maximum number of
A numerical study of the fragmentation of elongated polytropic axially symmetric clouds is presen... more A numerical study of the fragmentation of elongated polytropic axially symmetric clouds is presented. Results are obtained for various ratios of length to diameter L/D, polytropic constant gamma, and initial Jeans number J0. Initial density perturbations on the axis of otherwise uniformly dense cylinders are introduced, and the maximum number of fragments Nf(max) that can form and grow for combinations
A numerical study is presented of fragmentation in its simplest possible form: that of elongated,... more A numerical study is presented of fragmentation in its simplest possible form: that of elongated, isothermal, axially symmetric clouds. Results have been obtained for different ratios of length to diameter, L/D, and initial Jeans numbers, J0 (ratio of gravitational to thermal energies). Initial density perturbations are introduced on the axis of otherwise uniformly dense cylinders, and the maximum number of
Spectral data cubes of the interacting pair of galaxies NGC 2535 and NGC 2536 (the Arp 82 system)... more Spectral data cubes of the interacting pair of galaxies NGC 2535 and NGC 2536 (the Arp 82 system) targeting bright emission lines in the visible band, obtained with the imaging Fourier transform spectrometer (iFTS) SITELLE attached to the Canada–France–Hawaii Telescope (CFHT), are presented. Analysis of H$\alpha $ velocity maps reveals a bar in $\rm NGC\, 2536$. In $\rm NGC\, 2535$, we find strong non-circular motions outside the ocular ring, in the elliptical arc and tidal tails of $\rm NGC\, 2535$, and a misalignment between the kinematic and photometric position angles. We detect 155 H ii region complexes in the interacting pair of galaxies and determine oxygen abundances for 66 of them using different calibrators. We find, regardless of the indicator used, that the oxygen abundance distribution in $\rm NGC\, 2536$ is shallow, whereas in $\rm NGC\, 2535$, it is best fitted by two slopes, the break occurring beyond the ocular ring. The inner slope is comparable to the one observed...
Monthly Notices of the Royal Astronomical Society, 2019
SIGNALS, the Star formation, Ionized Gas, and Nebular Abundances Legacy Survey, is a large observ... more SIGNALS, the Star formation, Ionized Gas, and Nebular Abundances Legacy Survey, is a large observing programme designed to investigate massive star formation and H ii regions in a sample of local extended galaxies. The programme will use the imaging Fourier transform spectrograph SITELLE at the Canada–France–Hawaii Telescope. Over 355 h (54.7 nights) have been allocated beginning in fall 2018 for eight consecutive semesters. Once completed, SIGNALS will provide a statistically reliable laboratory to investigate massive star formation, including over 50 000 resolved H ii regions: the largest, most complete, and homogeneous data base of spectroscopically and spatially resolved extragalactic H ii regions ever assembled. For each field observed, three datacubes covering the spectral bands of the filters SN1 (363–386 nm), SN2 (482–513 nm), and SN3 (647–685 nm) are gathered. The spectral resolution selected for each spectral band is 1000, 1000, and 5000, respectively. As defined, the proj...
By implementing a dynamic wind-tunnel model in a smoothed-particle chemodynamic/hydrodynamic simu... more By implementing a dynamic wind-tunnel model in a smoothed-particle chemodynamic/hydrodynamic simulation suite, we have investigated the effects of ram pressure and tidal forces on dwarf galaxies similar to the Magellanic Clouds, within host galaxies with gas and dark matter halos that are varied, to compare the relative effects of tides and ram pressure. We concentrate on how the distributions of metals are affected by interactions. We find that while ram pressure and tidal forces have some effect on dwarf galaxy outflows, these effects do not produce large differences in the metal distributions of the dwarf disks other than truncation in the outer regions in some cases, and that confinement from the host galaxy gas halo appears to be more significant than ram pressure stripping. We find that stochastic variations in the star formation rate can explain the remaining variations in disk metal properties. This raises questions on the cause of low metallicities in dwarf galaxies.
Galaxies usually follow a mass–metallicity relation, where higher mass galaxies are typically mor... more Galaxies usually follow a mass–metallicity relation, where higher mass galaxies are typically more metal-rich than lower mass galaxies. Yet, tidal dwarf galaxies are outliers to this relation. These kinds of dwarfs are formed in galactic mergers. Since their material comes from the parent galaxies, they are typically more metal-rich than regular dwarfs. However, galaxies were far less enriched when the Universe was younger. One can ask if tidal dwarfs that formed at high redshift could be chemically distinguished from regular dwarfs. To answer this question, we performed a series of numerical simulations of gas-rich galaxy mergers at high redshift. We then identified the dwarf galaxies that formed in these mergers, and studied the evolution of their metal content. While the initial abundance of metals in the progenitors was low, the merger allows rapid enrichment and all tidal dwarf galaxies end up with high abundances. Their mass–metallicity relation is well fitted by the relation ...
The main goal of this paper is to compare the relative importance of destruction by tides, vs. de... more The main goal of this paper is to compare the relative importance of destruction by tides, vs. destruction by mergers, in order to assess if tidal destruction of dwarf galaxies in clusters is a viable scenario for explaining the origin of intracluster stars. We have designed a simple algorithm for simulating the evolution of isolated clusters. The distribution of galaxies in the cluster is evolved using a direct gravitational N-body algorithm combined with a subgrid treatment of physical processes such as mergers, tidal disruption, and galaxy harassment. Using this algorithm, we have performed a total of 227 simulations. Our main results are (1) destruction of dwarf galaxies by mergers dominates over destruction by tides, and (2) the destruction of dwarf galaxies by tides is sufficient to explain the observed intracluster light in clusters.
We simulate anisotropic outflows of AGN, and investigate the large-scale impact of the cosmologic... more We simulate anisotropic outflows of AGN, and investigate the large-scale impact of the cosmological population of AGN outflows over the Hubbl e time by performing NbodyΛCDM simulations. Using the observed quasar luminosity func tio to get the redshift and luminosity distribution, and analytical models for the outflow expansion, AGNs are allowed to evolve in a cosmological volume. By the present ep och, 13− 25% of the total volume is found to be pervaded by AGN outflows, with 10 −9 G magnetic field.
Monthly Notices of the Royal Astronomical Society, 2016
We performed a series of 29 gas dynamical simulations of disc galaxies, barred and unbarred, with... more We performed a series of 29 gas dynamical simulations of disc galaxies, barred and unbarred, with various stellar masses, to study the impact of the bar on star formation history. Unbarred galaxies evolve very smoothly, with a star formation rate (SFR) that varies by at most a factor of 3 over a period of 2 Gyr. The evolution of barred galaxies is much more irregular, especially at high stellar masses. In these galaxies, the bar drives a substantial amount of gas towards the centre, resulting in a high SFR, and producing a starburst in the most massive galaxies. Most of the gas is converted into stars, and gas exhaustion leads to a rapid drop of star formation after the starburst. In massive barred galaxies (stellar mass M * > 2 × 10 10 M) the large amount of gas funnelled towards the centre is completely consumed by the starburst, while in lower mass barred galaxies it is only partially consumed. Gas concentration is thus higher in lower mass barred galaxies than it is in higher mass ones. Even though unbarred galaxies funnelled less gas towards their centre, the lower SFR allows this gas to accumulate. At late times, the star formation efficiency is higher in barred galaxies than unbarred ones, enabling these galaxies to maintain a higher SFR with a smaller gas supply. Several properties, such as the global SFR, central SFR, or central gas concentration, vary monotonically with time for unbarred galaxies, but not for barred galaxies. Therefore one must be careful when comparing barred and unbarred galaxies that share one observational property, since these galaxies might be at very different stages of their respective evolution.
The gravitational instability of cosmological pancakes composed of collisionless dark matter in a... more The gravitational instability of cosmological pancakes composed of collisionless dark matter in an Einstein-de Sitter universe is investigated numerically to demonstrate that pancakes are unstable with respect to fragmentation and the formation of laments. A \pancake" is de ned here as the nonlinear outcome of the growth of a 1D, sinusoidal, plane-wave, adiabatic density perturbation. We have used high resolution, 2D, N-body simulations by the Particle-Mesh (PM) method to study the response of pancakes to perturbation by either symmetric (density) or antisymmetric (bending or rippling) modes, with corresponding wavevectors k s and k a transverse to the wavevector k p of the unperturbed pancake plane-wave. We consider dark matter which is initially \cold" (i.e. with no random thermal velocity in the initial conditions). We also investigate the e ect of a nite, random, isotropic, initial velocity dispersion (i.e. initial thermal velocity) on the fate of pancake collapse and instability. Our results include the following: (1) For \cold" initial conditions, pancakes are gravitationally unstable with respect to all perturbations of wavenumber k > 1 (where k = p = , and p and are the wavelengths of the unperturbed pancake and of the perturbation, respectively). This is contrary to the expectations of an approximate, thin-sheet energy argument applied to the results of 1D pancake simulations. The latter predicts that unstable wavenumbers are restricted to the range k min < k < k max , where perturbations with k < k min 1
Monthly Notices of the Royal Astronomical Society, Sep 27, 2019
The formation and evolution of local brightest cluster galaxies (BCGs) is investigated by determi... more The formation and evolution of local brightest cluster galaxies (BCGs) is investigated by determining the stellar populations and dynamics from the galaxy core, through the outskirts and into the intracluster light (ICL). Integral spectroscopy of 23 BCGs observed out to 4 r e is collected and high signal-to-noise regions are identified. Stellar population synthesis codes are used to determine the age, metallicity, velocity, and velocity dispersion of stars within each region. The ICL spectra are best modelled with populations that are younger and less metalrich than those of the BCG cores. The average BCG core age of the sample is 13.3 ± 2.8 Gyr and the average metallicity is [Fe/H] = 0.30 ± 0.09, whereas for the ICL the average age is 9.2 ± 3.5 Gyr and the average metallicity is [Fe/H] = 0.18 ± 0.16. The velocity dispersion profile is seen to be rising or flat in most of the sample (17/23), and those with rising values reach the value of the host cluster's velocity dispersion in several cases. The most extended BCGs are closest to the peak of the cluster's X-ray luminosity. The results are consistent with the idea that the BCG cores and inner regions formed quickly and long ago, with the outer regions and ICL forming more recently, and continuing to assemble through minor merging. Any recent star formation in the BCGs is a minor component, and is associated with the cluster cool core status.
A numerical study is presented of fragmentation in its simplest possible form: that of elongated,... more A numerical study is presented of fragmentation in its simplest possible form: that of elongated, isothermal, axially symmetric clouds. Results have been obtained for different ratios of length to diameter, L/D, and initial Jeans numbers, J0 (ratio of gravitational to thermal energies). Initial density perturbations are introduced on the axis of otherwise uniformly dense cylinders, and the maximum number of
A numerical study of the fragmentation of elongated polytropic axially symmetric clouds is presen... more A numerical study of the fragmentation of elongated polytropic axially symmetric clouds is presented. Results are obtained for various ratios of length to diameter L/D, polytropic constant gamma, and initial Jeans number J0. Initial density perturbations on the axis of otherwise uniformly dense cylinders are introduced, and the maximum number of fragments Nf(max) that can form and grow for combinations
A numerical study is presented of fragmentation in its simplest possible form: that of elongated,... more A numerical study is presented of fragmentation in its simplest possible form: that of elongated, isothermal, axially symmetric clouds. Results have been obtained for different ratios of length to diameter, L/D, and initial Jeans numbers, J0 (ratio of gravitational to thermal energies). Initial density perturbations are introduced on the axis of otherwise uniformly dense cylinders, and the maximum number of
Spectral data cubes of the interacting pair of galaxies NGC 2535 and NGC 2536 (the Arp 82 system)... more Spectral data cubes of the interacting pair of galaxies NGC 2535 and NGC 2536 (the Arp 82 system) targeting bright emission lines in the visible band, obtained with the imaging Fourier transform spectrometer (iFTS) SITELLE attached to the Canada–France–Hawaii Telescope (CFHT), are presented. Analysis of H$\alpha $ velocity maps reveals a bar in $\rm NGC\, 2536$. In $\rm NGC\, 2535$, we find strong non-circular motions outside the ocular ring, in the elliptical arc and tidal tails of $\rm NGC\, 2535$, and a misalignment between the kinematic and photometric position angles. We detect 155 H ii region complexes in the interacting pair of galaxies and determine oxygen abundances for 66 of them using different calibrators. We find, regardless of the indicator used, that the oxygen abundance distribution in $\rm NGC\, 2536$ is shallow, whereas in $\rm NGC\, 2535$, it is best fitted by two slopes, the break occurring beyond the ocular ring. The inner slope is comparable to the one observed...
Monthly Notices of the Royal Astronomical Society, 2019
SIGNALS, the Star formation, Ionized Gas, and Nebular Abundances Legacy Survey, is a large observ... more SIGNALS, the Star formation, Ionized Gas, and Nebular Abundances Legacy Survey, is a large observing programme designed to investigate massive star formation and H ii regions in a sample of local extended galaxies. The programme will use the imaging Fourier transform spectrograph SITELLE at the Canada–France–Hawaii Telescope. Over 355 h (54.7 nights) have been allocated beginning in fall 2018 for eight consecutive semesters. Once completed, SIGNALS will provide a statistically reliable laboratory to investigate massive star formation, including over 50 000 resolved H ii regions: the largest, most complete, and homogeneous data base of spectroscopically and spatially resolved extragalactic H ii regions ever assembled. For each field observed, three datacubes covering the spectral bands of the filters SN1 (363–386 nm), SN2 (482–513 nm), and SN3 (647–685 nm) are gathered. The spectral resolution selected for each spectral band is 1000, 1000, and 5000, respectively. As defined, the proj...
By implementing a dynamic wind-tunnel model in a smoothed-particle chemodynamic/hydrodynamic simu... more By implementing a dynamic wind-tunnel model in a smoothed-particle chemodynamic/hydrodynamic simulation suite, we have investigated the effects of ram pressure and tidal forces on dwarf galaxies similar to the Magellanic Clouds, within host galaxies with gas and dark matter halos that are varied, to compare the relative effects of tides and ram pressure. We concentrate on how the distributions of metals are affected by interactions. We find that while ram pressure and tidal forces have some effect on dwarf galaxy outflows, these effects do not produce large differences in the metal distributions of the dwarf disks other than truncation in the outer regions in some cases, and that confinement from the host galaxy gas halo appears to be more significant than ram pressure stripping. We find that stochastic variations in the star formation rate can explain the remaining variations in disk metal properties. This raises questions on the cause of low metallicities in dwarf galaxies.
Galaxies usually follow a mass–metallicity relation, where higher mass galaxies are typically mor... more Galaxies usually follow a mass–metallicity relation, where higher mass galaxies are typically more metal-rich than lower mass galaxies. Yet, tidal dwarf galaxies are outliers to this relation. These kinds of dwarfs are formed in galactic mergers. Since their material comes from the parent galaxies, they are typically more metal-rich than regular dwarfs. However, galaxies were far less enriched when the Universe was younger. One can ask if tidal dwarfs that formed at high redshift could be chemically distinguished from regular dwarfs. To answer this question, we performed a series of numerical simulations of gas-rich galaxy mergers at high redshift. We then identified the dwarf galaxies that formed in these mergers, and studied the evolution of their metal content. While the initial abundance of metals in the progenitors was low, the merger allows rapid enrichment and all tidal dwarf galaxies end up with high abundances. Their mass–metallicity relation is well fitted by the relation ...
The main goal of this paper is to compare the relative importance of destruction by tides, vs. de... more The main goal of this paper is to compare the relative importance of destruction by tides, vs. destruction by mergers, in order to assess if tidal destruction of dwarf galaxies in clusters is a viable scenario for explaining the origin of intracluster stars. We have designed a simple algorithm for simulating the evolution of isolated clusters. The distribution of galaxies in the cluster is evolved using a direct gravitational N-body algorithm combined with a subgrid treatment of physical processes such as mergers, tidal disruption, and galaxy harassment. Using this algorithm, we have performed a total of 227 simulations. Our main results are (1) destruction of dwarf galaxies by mergers dominates over destruction by tides, and (2) the destruction of dwarf galaxies by tides is sufficient to explain the observed intracluster light in clusters.
We simulate anisotropic outflows of AGN, and investigate the large-scale impact of the cosmologic... more We simulate anisotropic outflows of AGN, and investigate the large-scale impact of the cosmological population of AGN outflows over the Hubbl e time by performing NbodyΛCDM simulations. Using the observed quasar luminosity func tio to get the redshift and luminosity distribution, and analytical models for the outflow expansion, AGNs are allowed to evolve in a cosmological volume. By the present ep och, 13− 25% of the total volume is found to be pervaded by AGN outflows, with 10 −9 G magnetic field.
Monthly Notices of the Royal Astronomical Society, 2016
We performed a series of 29 gas dynamical simulations of disc galaxies, barred and unbarred, with... more We performed a series of 29 gas dynamical simulations of disc galaxies, barred and unbarred, with various stellar masses, to study the impact of the bar on star formation history. Unbarred galaxies evolve very smoothly, with a star formation rate (SFR) that varies by at most a factor of 3 over a period of 2 Gyr. The evolution of barred galaxies is much more irregular, especially at high stellar masses. In these galaxies, the bar drives a substantial amount of gas towards the centre, resulting in a high SFR, and producing a starburst in the most massive galaxies. Most of the gas is converted into stars, and gas exhaustion leads to a rapid drop of star formation after the starburst. In massive barred galaxies (stellar mass M * > 2 × 10 10 M) the large amount of gas funnelled towards the centre is completely consumed by the starburst, while in lower mass barred galaxies it is only partially consumed. Gas concentration is thus higher in lower mass barred galaxies than it is in higher mass ones. Even though unbarred galaxies funnelled less gas towards their centre, the lower SFR allows this gas to accumulate. At late times, the star formation efficiency is higher in barred galaxies than unbarred ones, enabling these galaxies to maintain a higher SFR with a smaller gas supply. Several properties, such as the global SFR, central SFR, or central gas concentration, vary monotonically with time for unbarred galaxies, but not for barred galaxies. Therefore one must be careful when comparing barred and unbarred galaxies that share one observational property, since these galaxies might be at very different stages of their respective evolution.
The gravitational instability of cosmological pancakes composed of collisionless dark matter in a... more The gravitational instability of cosmological pancakes composed of collisionless dark matter in an Einstein-de Sitter universe is investigated numerically to demonstrate that pancakes are unstable with respect to fragmentation and the formation of laments. A \pancake" is de ned here as the nonlinear outcome of the growth of a 1D, sinusoidal, plane-wave, adiabatic density perturbation. We have used high resolution, 2D, N-body simulations by the Particle-Mesh (PM) method to study the response of pancakes to perturbation by either symmetric (density) or antisymmetric (bending or rippling) modes, with corresponding wavevectors k s and k a transverse to the wavevector k p of the unperturbed pancake plane-wave. We consider dark matter which is initially \cold" (i.e. with no random thermal velocity in the initial conditions). We also investigate the e ect of a nite, random, isotropic, initial velocity dispersion (i.e. initial thermal velocity) on the fate of pancake collapse and instability. Our results include the following: (1) For \cold" initial conditions, pancakes are gravitationally unstable with respect to all perturbations of wavenumber k > 1 (where k = p = , and p and are the wavelengths of the unperturbed pancake and of the perturbation, respectively). This is contrary to the expectations of an approximate, thin-sheet energy argument applied to the results of 1D pancake simulations. The latter predicts that unstable wavenumbers are restricted to the range k min < k < k max , where perturbations with k < k min 1
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